Known large-scale telemetry systems are based on the mobile communications network of GSM (Global System for Mobile Communications) type. These systems are, for example, systems for reading water, electricity or gas meters or even systems for monitoring resources of a community such as irrigation, pollution, parking spaces, etc.
In these systems, the sensors are equipped with a GSM communication module and transmit measurement readings at regular intervals to a base station capable of processing the information received.
Depending on the systems, the information is either transmitted following a request sent regularly by the base station, or transmitted directly by the sensors.
The information may be encrypted to ensure its confidentiality.
The encryption techniques protect the content of the information but are ineffective against interception and scrambling attacks.
There are, moreover, techniques for protecting against scrambling, notably in the military field. Such techniques are applied to the communication protocol used on a communication link at the physical layer level. One known technique consists, for example, in spreading the spectrum. Such a modification applied to a standardized protocol, such as, for example, the GSM protocol, requires an adaptation of the standard.
These techniques are too complex and too costly to be implemented in a telemetry system comprising a large number of sensors.
There is therefore a need for a simple solution for protecting a telemetry system against interception and/or scrambling attacks.